Sound

Harleen Saini 21 December 2018

When you think of sound, what’s the first thing that pops into our head? Maybe you think of that song you heard on the radio this morning, or that song you sang in the shower. But have you ever thought about what exactly sound is? Have no fear, because this article will answer just that!

Anatomy of the Ear

Before we delve into the topic of sound, I think we should take a quick look at our ears. After all, this is how we hear. Below is an image to help explain some basics:

We won’t go into too much detail, but let’s look at an example of what happens when you hear someone talking. The movements of their mouth create ‘waves’ of moving air which travel into your ear canal and into the eardrum. This causes small bones called ossicles to vibrate. The movement of the ossicles sends the wave signals into the cochlea(the snail-shaped purple structure in the image). Inside the cochlea, you have small little cells called hair cellswhich then send the signals to the brain. This is what allows you to process and actually hear that person’s voice!

Sound Waves

As you just learned, we hear sound and noise from our ears whenwavesare produced by objects that are “vibrating.”Specifically, when this vibration occurs, it forces the air it hits in its path to move by compressing it and creating a sort of pressure. This causes areas of high and low pressure as the sound moves towards our ears.

Imagine this kind of a like a metal spring, like a Slinky toy. When you push one side of the Sslinky, it causes an area to bunch up. This is similar to the areas of high pressure. Since you pushed one side of it, the motion causes the bunching areas to slowly travel down until it reaches the end. You will notice that the area that had been bunched up will then stretch (similar to the areas of low pressure) as the motion continues. In other words, certain areas bunch up, while others stretch out, all the way until it reaches the end.

This can still be hard to imagine, so here is an animation of what sound actually looks like at an atomic level. As you can see in the image, you have areas that bunch up (high pressure) and areas that are stretched out (low pressure).

Pitch and Frequency

Sound can vary depending on its pitch or frequency. Frequencyis the rate at which waves are made and is measured in Hertz (Hz). 1Hz is also the same as saying one cycle (in this case a sound wave) per second..

A pitch is often determined by frequency. The Oxford dictionary defines pitch as “a sound that is determined by the vibration rate made by the sound source.”

Let’s look at some examples to think about this. Imagine you hear a very deep, low note, maybe from a bass guitar or a key at the lower end of a piano. This note has low frequency and is low pitched.

Now imagine you hear a very high, bright note, maybe from a violin or the higher end of a piano. This note has a higher frequency and is high-pitched.

Did you know? Frequencies too low for us to hear (lower than 20Hz) are called infrasonic, while frequencies too high to hear (above 20,000 Hz) are called ultrasonic.

In general, a healthy human has a hearing range of about 20-20,000 Hz. But that doesn’t necessary mean that a sound at 20,000 Hz is comfortable or even safe to listen to! Click here to learn about the positive and negative effects of noise.

Did you know? Dogs have a hearing range of 40-60,000 Hz! They can hear a wider range of high frequency sounds compared to humans. Not surprisingly, dog whistles have very high frequencies. This is why when someone plays a dog whistle, our canines go crazy but we don’t hear a thing!

Harleen Saini

Hello everyone! I am a premedical student from the United States who is hoping to become a physician one day. My love for science began with watching shows such as Bill Nye the Science Guy and The Magic School Bus series. These helped make science fun and exciting, and eventually led me to pursue an undergraduate degree in Biological Sciences which I completed in 2016. I enjoy being able to share my passion for STEM topics, especially health science and biology, and hope to help others fall in love with the sciences as well. Outside of this, I am also a musician, enjoy dancing and love to learn foreign languages!